This was a significant element in Tad Williams' series of novels, Otherland. The intended use of VR was one of the major focal points of the book, and since he was protraying a world in which VR had taken the place of our modern day computers, he did explore the possibilities of using VR for things besides its intended purpose.

One of the societal elements in Otherland is the chargeheads, people who use bootleg or amateur-made VR gear to over-stimulate certain centers of their brains beyond the range of normal sensory input. The result was somewhat similar to highly potent narcotics...complete with emotional dependecy and addiction. People would have chargers implanted in their neck. Prolonged used of the chargers would result in brain damage. Government-sponsed programs would force addicts to have their neurocannulae removed (a neurocannula being the fictional "jack" where you'd plug in the VR input) to prevent future use of chargers (or the VR net in general.)

The whole story of Otherland really revolves around the super-complex VR network called Otherland, which is somehow able to override any of the limitations of cheaper, low-end VR gear and draw its (sometimes unwilling) users into an incredibly realistic universe. I won't say more, for fear of spoiling Otherland for anyone who hasn't it. However when, and if, we as a society eventually develop a VR interface, it will never be intended to mimic reality so exactly. How would we tell the difference? It would always be different, graphically, than real life just to prevent the disturbing notion that one could be trapped inside a reality which was not reality...à la The Matrix. Seemingly, that would be the most heinous unintended use of VR.